compute the power level of ambiant noise using mems microphones

Question

I' m using digital microphone (MEMS) on STM32 discovery board Fto record ambiant noise, and I need to know how to convert the samples amplitude to power level in dB SPL.

the microphone that I 'm using is the MP45DT02, in the datasheet the sensibility of the mic is -26 dBFS and the SNR is 61 dB

Answer 1

What the senstivity means is that a 94 dBSPL sine input will give a -26dBFS peak output level, or a -29 dBFS rms output level. Unless your signal is a sine wave it's probably makes more sense to use rms.

1. Measure the RMS of the signal.
2. Convert the RMS value to dBFS (dBFS = 20*log10(rms)))
3. Convert the dBFS value to dBSPL using the relationship of -29 dBFS = 94 dBSPL. For example, if you measured -50 dBFS then you are 21 dB down from -29. 94-21 = 83 dBSPL and there's your answer.